This description relates to adjusting dynamic range for audio reproduction signals.
In many situations in which people listen to recorded or broadcast speech or music, it is difficult to hear both the loud portions of the program and the soft portions with the same volume control setting. In a noisy listening environment (e.g., the passenger cabin of an automobile), when the loud passages are turned up high enough to be audible over the noise, the soft passages are masked by noise, and are inaudible. This situation is especially problematic with orchestral music, which can have a dynamic range of over 80 dB. In quiet listening situations (e.g., listening at home late at night), when soft passages are set at a comfortable background listening level, the loud passages can be loud enough to wake other family members or neighbors.
Furthermore, constantly changing noise levels provide an even more disagreeable listening experience. In a moving automobile, opening a window can drastically change the level and spectrum of the noise in a matter of a second. In a restaurant playing background music for patrons, the noise may noticeably change from the beginning of the evening to the end, as more and louder patrons fill the restaurant.